Electric discharge lamp



Dec. 13, 1955 WEBB ETAL ELECTRIC DISCHARGE LAMP Filed Feb. 6, 1951 n Q V .b@ m 3 0 e 0 ow w B AG A Vfidfi I AM w United States Patent ELECTRIC DISCHARGE LAMP Alan Arthur Webb, Surbiton, and Eric John George Beeson, Southwell, England, assignors to General Electric Company, a corporation of New York Application February 6, 1951, Serial No. 209,642

Claims priority, application Great Britain March 3, 1950 3 Claims. (Cl. 315-58) This invention relates to electric discharge lamps of the compact source type, that is, of the kind comprising electrodes, constituted of a refractory metal, and usually relatively massive, spaced apart a distance short compared with the diameter of a substantially spherical envelope in which they are contained, the envelope being filled with a rare gas which, during the operation of the lamp, exerts a pressure of several atmospheres.

In lamps of the kind with which the invention is particularly concerned, that electrode which is to serve as the anode is commonly made more massive than the cathode and the lamp is operated from a D. C. supply. In order to initiate a discharge in the lamp, it is necessary either to supply momentarily between anode and cathode a voltage many times greater than that required to support a discharge, or to create local ionization at the cathode by applying a transient voltage between an auxiliary electrode located close to the cathode. This transient voltage may be in the form of a high frequency pulse as disclosed in British patent specification No. 545,388.

In view of the high pressure which obtains during operation, the envelopes of such lamps are generally made of fused quartz, since this is one of the few materials which possess the necessary translucency, strength, and ability to withstand the high temperatures involved. Owing to the difiiculty of forming the vacuum-tight seals required for leading through the wall of the envelope the conductors necessary for supporting and conducting current to the electrodes, the additional seal required for an auxiliary electrode for discharge-initiating purposes constitutes a serious disadvantage, which it is the object of the present invention to remove.

According to the invention, a discharge lamp of the kind set forth above is provided with an auxiliary electrode extending into the neighborhood of one of the main electrodes, the auxiliary electrode being supported within the envelope by conductive means extending into, but not through, the wall of the envelope at a region displaced from the leading-in conductor to that one of the main electrodes, whereby a voltage pulse can be created at the auxiliary electrode by means external to the envelope but possessing capacity to the said conductive means greater than it possess to the lead-in conductor.

When the lamp is one constructed so that one of the main electrodes is especially adapted to constitute the cathode, the auxiliary electrode, hereinafter referred to as the probe, will extend into the neighborhood of that electrode. Since it is the function of the lamp to emit light, and it will usually be desirable to use the lamp in association with light-directing means, such as a reflector, it is desirable that the probe be so positioned that it will obstruct as little light as possible. This means that it should be located as near to the main electrode with which it is associated as is consistent with the necessity of being able to couple capacitively to it from outside the envelope. To this end the probe may consist of a wire extending at an angle of about 45 to the leading-in con ice ductor to that electrode and at its top spaced from the main electrode by a distance of about 1 mm.

To enable the invention to be readily understood we will now refer to the accompanying drawing which shows, in Figs. 1 and 2, sectional elevations of a construction which may be adopted for the lamp with two diiferent ways of applying a pulse voltage to the probe.

It will be seen from the drawing that the lamp cornprises a substantially spherical envelope 1 into which, at diametrically opposite points, are sealed conductors supporting an anode 2 and a cathode 3. This constitutes a well-known construction for lamps of the kind to which the invention relates. According to the invention an auxiliary electrode 4, the probe, is supported Within the envelope by conductive means extended into, but not through, the wall of the envelope. In the arrangement illustrated, the probe 4 is in the form of a wire extending at an angle of about 45 to the support for the cathode and embedded in the wall of the envelope, the tip of the wire being spaced from the cathode by about 1 mm.

To apply the voltage pulse between the probe and the cathode, We may, as shown in Fig. 1, encircle the envelope with a wire or band 5 and apply the pulse thereto. It is believed that, when the pulse is applied to the wire or band, charges are produced which arrive at the probe as a result of the greater proximity of the wall end of the probe 4 to the wire 5, and produce a high potential gradient between the tip of the probe and the cathode and cause ionization. It is thus desirable to position the wall end of the probe as far away from the seal to the adjacent main electrode (the cathode in the arrangement shown) consistent with ensuring that the probe does not unduly obstruct light. It is thus preferable to locate the probe in a plane which contains the axis of the cathode and its support.

In the arrangement of Fig. 2, a metal cap 6 is supported on the outside of the envelope in proximity to the wall end of the probe to form a capacitive means whereby the pulse voltage can be caused to energize the probe.

The invention is of particular value in connection with compact source discharge lamps having a filling of xenon and no metal vapor, and has been found to operate satisfactorily with a lamp having an envelope of about 1.5 inches diameter, an electrode spacing of about 18 millimeters and a pressure of xenon of about 2 to 3 atmospheres at room temperature.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A high pressure gaseous electric discharge lamp comprising a sealed envelope of quartz, a pair of cooperating main electrodes in said envelope, lead-in conductors supporting said electrodes and extending through said envelope to the exterior thereof, and an auxiliary electrode of wire-like form having one end extending into proximity to one of said main electrodes and having its other end extending into and terminating within the wall of the envelope at a region displaced appreciably from the lead-in conductor to the said one main electrode, and means external to the envelope but possessing capacity to the said conductive means greater than it possesses to the last-mentioned lead-in conductor for creating a voltage pulse at the said auxiliary electrode.

2. A high pressure gaseous electric discharge lamp comprising a substantially spherical envelope of quartz, a pair of cooperating main electrodes in said envelope, lead-in conductors supporting said electrodes and extending through said envelope to the exterior thereof at substantially diametrically opposite points, and an auxiliary electrode of wire-like form having one end extending into proximity to one of said main electrodes and disposed at an angle of about 45 with the lead-in conductor connected to the said one main electrode and having 3 its other end extending into and terminating within the wall of the envelope,.and means external to the envelope but possessing capacity to the said conductive means greater than it possesses to the last-mentioned lead-in conductor for creating a voltage pulse at the said auxiliary electrode.

3. A high pressure gaseous electric discharge lamp comprising a substantially spherical sealed envelope of quartz, a pair of cooperating main electrodes in said-envelope and spaced apart a distance short compared with the diameter of said envelope, lead-in conductors supporting said electrodes and extending through said envelope, a filling of rare gas in said envelope at a pressure of several atmospheres, and an auxiliary electrode of wire-like form having one end extending into proximity toone of said mainelectrodes and having the other end extending into and terminating within the wall of the envelope at a region displaced appreciably from the lead-in conductor to the said one main electrode, and means external to the envelope but possessing capacity I to the said auxiliary electrode greater than it possesses to the last-mentioned lead-in conductor for creating a voltage pulse at the said auxiliary electrode.

References Cited in the file of this patent UNITED STATES PATENTS 1,488,337 Gernsback Mar. 25, 1924 1,832,212 Jacobsen Nov. 17, 1931 2,020,393 Woolrich Nov. '12, 1935 2,038,049 Kirsten Apr. '21, 1936 2,087,735 Pirani July 20, 1937 2,207,133 Scott. July .9, .1940 2,241,968 Suits May 13, 1941 2,265,396 Reger -a Dec. 9, 1941 2,289,346 Craig et a1. July 14, 1942 2,447,377 Tognolg et a1. Aug. 17, 1948 FOREIGN PATENTS 573,141 GreatBritain Oct. 8, 1945 

